Interaction of Epicutaneously Applied Lipids with Stratum Corneum Depends on the Presence of either Emulsifiers or Hydrogenated Phosphatidylcholine

Abstract

The barrier function of the stratum corneum (SC) significantly determines the interaction of epicutaneously applied substances with the skin organ. Although the exact molecular processes are still unclear, it is undoubted that the intercellular lipid composition and order of the SC is significantly involved in this interaction. Topically substituted phases, especially those of lipophilic composition, seem to interact very intensely with lipid membranes; they can be integrated, form separate phases, or even permeate through the SC into the viable skin. The latter is not desired, especially in barrier-protective preparations with a lipophilic phase. The present paper investigates the penetration behavior of topically applied, DiI-labeled lipids into human ex vivo skin depending on the phase organization of different o/w emulsifiers compared to emulsifier-free preparations containing hydrogenated phosphatidylcholine by means of fluorescence indication. Results are presented for intact and defined damaged epidermal barrier. In addition, the washout effect based on skin samples treated by artificial watering after lipid incubation, and the influence of the phase transition temperature of the SC membrane were studied. The results show that in intact and damaged skin, the penetration depth of the lipids increases directly proportionally with the hydrophilic-lipophilic balance (HLB value), while the washout effect and the HLB value proved to be inversely related. An increase in penetration depth with higher HLB values was also apparent when the phase transition temperature of the physiological membranes was exceeded. Altogether, the results clearly demonstrate that the characteristics of the emulsifying phase of a preparation significantly determine the interaction of a substituted lipophilic phase with the SC. Especially bipolar lipids, like phosphatidylcholines, showed intradermal dispersion patterns which hint at an especially intense interaction with physiological membranes.

Influence of Different Cosmetic Formulations on the Human Skin Barrier

“…The TEWL would be decreased, but positive effects also take time. The DMS showed a positive barrier-stabilizing effect and the more damaged the skin, the greater the effect [14,15]. …”

Drug Delivery with Topically Applied Nanoparticles: Science Fiction or Reality?

“…In the past, it had been assumed that topically applied substances penetrate exclusively via the intercellular route, i.e., inside the lipid layers around the corneocytes [27,28,29]. Recently it was demonstrated that the hair follicles represent an efficient penetration pathway for topically applied substances [30,31,32].…”

Präklinische und klinische Validierung der kutanen Bioverfügbarkeit der hydrophilen Phase einer W/O‐Emulsion

“…Da gängige Öle nicht oder nur sehr gering in das SC eindringen, wird diese Strategie auch als „äußere Okklusion“ bezeichnet . Demgegenüber interagieren präformierte Phosphatidylcholinmembranen sehr wohl mit dem SC, werden aber durch Phasenseparation nicht wesentlich in die natürlichen Membranen integriert, was zur Bezeichnung „innere Okklusion“ geführt hat . Je nach galenischer Konzeption eines Präparates werden die beschriebenen Effekte ermöglicht und eine Hydratation des SC ggf.…”